The present invention relates to intraluminal therapy devices and more particularly to catheters intended for use in angioplasty and brachytherapy.
Stenosis is a narrowing or constriction of a duct or canal. A variety of disease processes, such as atherosclerotic lesions, immunological reactions, congential abnormalities and the like, can lead to stenoses of arteries or other vessels. Stenosis of a coronary artery can reduce blood flow sufficiently to cause myocardial ischemia. Percutaneous transluminal coronary angioplasty (PTCA), the insertion and inflation of a balloon catheter in a coronary artery to affect its repair, is widely accepted as an option in the treatment of obstructive coronary artery disease. In general, PTCA is used to increase the lumen diameter of a coronary artery that is partially or totally obstructed by a build-up of cholesterol fats or atherosclerotic plaque. In PTCA, a coronary guiding catheter provides a channel from outside the patient to the ostium of a coronary artery. A balloon catheter is advanced over a small diameter, steerable guidewire through the guiding catheter, into the artery, and across the stenosis. The tubular balloon near the tip of the catheter is inflated to expand the narrowing. Dilation of the occlusion, however, can form flaps, fissures and dissections which threaten abrupt reclosure of the dilated vessel or even perforations in the vessel wall. To treat or prevent such sequelae, tubular stents are often placed within the angioplasty site to scaffold the vessel lumen. Since a tubular balloon typically occludes, or shuts off blood flow through an artery, angioplasty can be conducted for only short periods before the lack of blood flow may cause ischaemia or tissue damage. To solve this problem, some PTCA catheters include a bypass, or perfusion channel, so that blood continues to flow through the artery during dilatation.
In some devices, the perfusion channel is a hollow shaft extending through the balloon. Blood ingress to and egress from the hollow shaft is provided by open ports in the shaft, located proximal and distal to the balloon. In other PTCA catheters, a helical balloon mounted around the catheter shaft forms a spiral perfusion channel between the wall of the vessel and the inflated balloon. The flow rate of blood passing through the spiral channel depends upon the channel cross sectional area, which is related, in part, to the channel width between adjacent turns of the helical balloon. However, widening the channel width to increase flow also decreases the surface area of the stenosis that is exposed to the dilating force of the helical balloon. Thus, there are design trade-offs that attend dilatation balloon catheters having spiral perfusion channels. In other prior art perfusion angioplasty catheters, the catheter shaft is mounted off-center within a coiled balloon such that blood can flow through the center of the coil.
Other intraluminal therapies include atherectomy (mechanical removal of plaque residing inside an artery), laser ablative therapy and the like. While the stenosis or occlusion is greatly reduced using these therapies, many patients experience a recurrence of the stenosis over a relatively short period. Restenosis, defined angiographically, is the recurrence of a 50% or greater narrowing of a luminal diameter at the site of a prior therapy. Additionally, researchers have found that angioplasty or placement of a stent in the area of the stenosis can irritate the blood vessel and cause rapid reproduction of the cells in the medial layer of the blood vessel, developing restenosis through a mechanism called medial hyperplasia. Restenosis is a major problem which limits the long-term efficacy of invasive coronary disease therapies. Additionally, the rapid onset of restenosis is compounded by the lack of ability to predict which patients, vessels, or lesions will undergo restenosis.
Although the mechanism of restenosis is not fully understood, clinical evidence suggests that restenosis results from a migration and rapid proliferation of a subset of predominately medially derived smooth muscle cells, which is apparently induced by the injury from the invasive therapy. Such injury, for example, is caused by the angioplasty procedure when the balloon catheter is inflated and exerts pressure against the artery wall, resulting in medial tearing. It is known that smooth muscle cells proliferate in response to mechanical stretching and the resulting stimulation by a variety of growth factors. Also, intimal hyperplasia can contribute to restenosis, stimulated by the controlled therapeutic injury. It is believed that such proliferation stops one to two months after the initial invasive therapy, but that these cells continue to express an extracellular matrix of collagen, elastin and proteoglycans. Additionally, animal studies have shown that during balloon injury, denudation of endothelial cells can occur, followed by platelet adhesion and aggregation, and the release of platelet-derived growth factor (PDGF) as well as other growth factors. As mentioned above, this mass of tissue can contribute to the re-narrowing of the vascular lumen in patients who have restenosis. It is believed that a variety of biologic factors are involved in restenosis, such as the extent of the tissue injury, platelets, inflammatory cells, growth factors, cytokines, endothelial cells, smooth muscle cells, and extracellular matrix production, to name a few.
It has been found that irradiating the blood vessel walls at the treatment site can reduce or prevent hyperplasia. Precise control over the amount of radiation is important, since insufficient radiation will not prevent restenosis and excessive radiation can further damage the blood vessel or surrounding tissues. To prevent unnecessary radiation beyond the site of the stenosis, it is preferable to introduce a small radiation source into the treated vessel. The prior art contains numerous examples of brachytherapy catheters and radiation sources for this purpose. One type of known devices is a catheter that delivers to the treatment site a linear radioactive filament, or radioactive guidewire source.
Another known prior art device is a catheter having a spherical inflatable chamber adjacent the catheter distal end. A fluid containing a radioactive material is pumped into the chamber, inflating the chamber and treating the vessel walls with ionizing radiation. The chamber can be inflated against the vessel wall, displacing any blood that may attenuate irradiation of the tissue by the radiation fluid source within the chamber. Irradiating a segment of an artery or the like generally takes from about 3 to 45 minutes. As happens in angioplasty, however, inflating the chamber against the vessel wall will stop blood flow, so it can be inflated only for a short time. There are known brachytherapy catheters that include a perfusion channel formed through the center of a stack of toroidal elements that can be inflated with radiation fluid. The complexity of making such a device, and its requirement for a cumbersome sheath to envelope the inflation element during its placement in the vessel are significant disadvantages.
Furthermore, in all prior art perfusion angioplasty catheters, the perfusion feature is built-in, such that the clinician needs to pre-select such a catheter before beginning the treatment procedure. Therefore, any design trade-offs, such as greater deflated profile or complicated structure, must be accepted and planned for, or else a catheter exchange is required. What is needed is a device that is capable of state-of-the-art angioplasty or brachytherapy with perfusion that is selectively available during the procedure, should the need arise.
The use of prior art angioplasty and brachytherapy catheters in the same patient has typically required exchanging one type of device for the other, which can be tedious and time-consuming. Thus, it is an object of the invention to provide a single device that is capable of performing both angioplasty and brachytherapy.
A further object of the invention is to provide a device that is capable of performing angioplasty and brachytherapy simultaneously.
Another object of the invention is to provide an intraluminal therapy catheter that is capable of selectively forming a perfusion channel during treatment.
The present invention is an intraluminal therapy catheter having at least two inflatable treatment members disposed near the distal end of the catheter. A first treatment member is helically mounted about the shaft of the catheter and forms a helical perfusion channel when inflated into contact with the vessel being treated.
In a first embodiment of the invention, the second treatment member is also helically mounted about the catheter shaft and is also capable of forming a helical perfusion channel when inflated into contact with the vessel. The first and second treatment members are intertwined to form a double helix configuration wherein each member is capable of being inflated to generally fill the helical perfusion channel created by simultaneous inflation of the other member. In this embodiment, simultaneous inflation of both treatment members forms a generally cylindrical treatment body. Either treatment member can be selectively deflated to leave a helical perfusion channel formed by the other, still inflated, treatment member. Both treatment members are deflated to a low profile configuration during insertion and withdrawal of the catheter from the patient.
The first embodiment of the invention has several useful modes of operation. In a first mode, simultaneous inflation of both treatment members provides generally cylindrical dilation of a diseased blood vessel, comparable to PTCA with a single tubular balloon. Advantageously, in a second mode of operation, if the patient experiences discomfort due to ischaemia, a first helical treatment member can be deflated to form a perfusion channel, while the second treatment member remains inflated to continue dilation of the vessel, albeit in a helical pattern. Blood flowing through the perfusion channel can alleviate the patient""s discomfort, as described above. If so desired, the first helical treatment member can be re-inflated while the second helical treatment member is deflated, such that no part of the vessel wall is untreated, and distal perfusion can be provided throughout the procedure.
In a third mode of operation of the first embodiment, the treatment members are simultaneously inflated with radioactive fluid to provide brachytherapy to the treatment area, as may be desired following a procedure such as PTCA. In a fourth mode of operation, comparable to the second mode described above, the treatment members may be deflated individually, and/or alternatively to provide complete brachytherapy treatment while alleviating ischaemia, as necessary.
In a fifth mode of operation of the first embodiment, the first treatment member is inflated to dilate the diseased vessel and the second treatment member is inflated with radioactive fluid simultaneously with, or immediately following the dilation provided by the first treatment member.
In a second embodiment of the invention, the second treatment member is a tubular balloon mounted generally coaxially about the catheter shaft, adjacent to the first treatment member. Using this structure, the second treatment member can perform angioplasty and the first treatment member can perform brachytherapy immediately afterwards, without having to make a catheter exchange. After the PTCA balloon is deflated, the catheter is moved sufficiently to position the first treatment member within the dilated portion of the vessel, then the first treatment member is inflated with radioactive fluid.
In all of the embodiments and modes of operation described above, if dilation is the intended function, then the treatment member is fabricated from inelastic polymeric material, comparable to PTCA balloons. If brachytherapy is intended, then optionally, the treatment member can be fabricated from elastic material.